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    Heating your boat with electricity, how it really works.

    I am sitting in my boat right now and the temperatre outside is a brisk 33 degrees. I’m thinking of all the other liveaboards, and wondering if they are warm wherever they are.
    Are they heating with electricity? If so, how is it working out?

    So... Lets go over some of the basics regarding Electric Heat.

    Most shore power connections are 30 AMP at 120 volts. Doing some quick math of 30*120 shows us that ashore power connection can supply at a maximum of 3600 watts. Each WATT over the course of an hour is 3.41 BTU.

    That means at maximum a shore power connection can supply 12,276 BTU’s per hour.

    That’s nice, but what does all that mean to a boater just trying to stay warm?

    Lets think in terms of electric heaters. Most electric heaters have a couple settings. Low which is about 700 watts, and high which is about 1500 watts.

    This means that in theory we could use five 700 watt heaters, or two 1500 watt heaters. That in theory part is how boat fires happen. The challenge is that the shore power connection while being rated at 30 amps cannot actually supply 30 amps all the time, like it is asked to do on a cold night. The problem is shore power connectors age, and they get loose, and they get a bit of corrosion, and they loose their ability to safely carry a 30 amp load.

    The same issue applies to the wiring inside a boat. That electrical receptical you are plugging the heater into might have been able to supply that 1500 watt heater back when your boat was made, but it probably cannot supply that much power today, especially for a long period of time like a heater requires.

    So... If you are heating with electricity, there are a couple of tricks that might just save your life.
    First, do not use 1500 watt heaters. Use more heaters on a lower setting.
    2nd, replace your old shore power connection and cord. A worn shore power connection will get hot and cause a fire.
    3rd, feel your shore power connection frequently. If it is warm to the touch that is a huge danger sign.
    4th, do not overload your shore power connection. Do not run it at a full 30 amps all night long. You are asking for trouble, big trouble.

    Now back to the original question, can you heat the average boat with a properly maintained 30 amp shore power connection at below freezing temperatures?

    That depends on the size of the boat of course, but I cannot keep my Bayliner 4788 warm at freezing temperatures using a 30 amp shore power connection. How do I know this??? Well my boat has four 700 watt electric heaters built in from the factory. with all four running my boat is not comfortable at night at 32 degrees. Yes it is tolerable with a sweater and socks and sweat pants on, but it requires that to stay warm. I have diesel heat though. A total of 27,000 BTU per hour. That makes a huge difference, but then again I’m in Alaska, and it gets cold here.

    There you go, some food for thought, and some ideas thast might just keep you alive if you are heating with electricity.


    KEVIN SANDERS
    4788 LISAS WAY - SEWARD ALASKA
    where are we right now​​​​​​???​

    https://share.findmespot.com/shared/...j23OquWOj2N3Xe

    #2
    I have read and practice the Boeshield defense. My outlet (where the boat plugs in) is sprayed semi-regularly. Every three months at least I spritz the female end. Anecdotal evidence shows that boats who do practice this preventative maintenance do not have issues. That is not to say an overload cannot cause a problem. It will. Still, folks have convinced me that this is good practice.

    Aboard Seaweed I did replace my power inlet several years ago. She was 25 years old at that point and I thought that was a Good Idea.

    Thanks for the information on electric heating via a 30A power supply. That is interesting.

    Comment


      #3
      When I lived on a 34’ sail boat, I had a 1500w heater in the bow and a 700w heater in the stern. This ment l was pulling 11 amps in the bow 6 amps in the stern, 11 amps when the water heater was on and 2 amps with lights and things. That’s a total of 30 amps. I never tripped the breaker but I did burn up a 10 gauge wire to the master panel and I did burn up a shore power cord.

      On my 42’ power boat I used a 50a 125-250 power supply. One leg was dedicated to house including hot water. It had a 30 amp master breaker. The other leg ran three 1500w heaters, two full time and one rarely. That’s a total of 30 amps on a 50 amp cord. Over the course of 15 years I suffered a failure of the female unit on the dock. I don’t know if the failure was socket related or wiring to the socket but it was not a failure of my cord.

      30 amp cords are rated for max use. NOT CONTINUOUS USE. If you pull 30 amps all winter, something will fail.
      Azzurra
      Seattle, WA
      Ocean Alexander 54

      Comment


        #4
        Originally posted by Tiltrider1 View Post
        When I lived on a 34’ sail boat, I had a 1500w heater in the bow and a 700w heater in the stern. This ment l was pulling 11 amps in the bow 6 amps in the stern, 11 amps when the water heater was on and 2 amps with lights and things. That’s a total of 30 amps. I never tripped the breaker but I did burn up a 10 gauge wire to the master panel and I did burn up a shore power cord.

        On my 42’ power boat I used a 50a 125-250 power supply. One leg was dedicated to house including hot water. It had a 30 amp master breaker. The other leg ran three 1500w heaters, two full time and one rarely. That’s a total of 30 amps on a 50 amp cord. Over the course of 15 years I suffered a failure of the female unit on the dock. I don’t know if the failure was socket related or wiring to the socket but it was not a failure of my cord.

        30 amp cords are rated for max use. NOT CONTINUOUS USE. If you pull 30 amps all winter, something will fail.


        That is a great way to describe a 30 amp shore power connection

        KEVIN SANDERS
        4788 LISAS WAY - SEWARD ALASKA
        where are we right now​​​​​​???​

        https://share.findmespot.com/shared/...j23OquWOj2N3Xe

        Comment


          #5
          Kevin - Your diesel heat is FHA, correct? I have a few questions. How many supply and returns do you have? Where are they located?

          Assuming 32*F and interior temp 68*F what's the duty cycle of the furnace and is 27K enough [no electric heat supplement]

          Thanks!
          1989 Bayliner 4588
          Portsmouth, NH

          Comment


            #6
            Originally posted by Irony
            Kevin - Your diesel heat is FHA, correct? I have a few questions. How many supply and returns do you have? Where are they located?

            Assuming 32*F and interior temp 68*F what's the duty cycle of the furnace and is 27K enough [no electric heat supplement]

            Thanks!
            My furnaces are Wallas Forced air. I chose the Wallas units because of their quietness, and i really liked the cool to the touch exhaust tube.

            Since you are familiar with the 45/47 Bayliner/meridian 490 I’ll describe my setup.

            The salon is served by a Wallas 30DT 10,000 btu furnace located behind the settee in the corner. In the 4788 this is in the aft starboard corner of the salon. There is a register right near the door, and another near the forward part of the settee. One return is in the settee, very near the inside corner. The other return is not hooked up, so it pulls in air adjacent to the furnace. There is a outside vent to the cockpit from that area bringing in fresh air.

            The lower cabins were more difficult. The Wallas 30DT 10,000 btu unit is located under the pilothouse settee. The ducts run down, behind the fridge, and into the mid berth. One duct comes out just above the mid berth closet. The other duct runs under the mid berth bunk, and under the bunk bed berth lower bunk with a tee and outlet in tee bunk berth. It then goes forward and has an outlet in the master stateroom. The return for this is directly into the pilothouse, with no provison for fresh air mixing.

            The pilothousehas a Wallas 22DT 7,500 BTU furnace. This is located behind the pilothouse dash, in that huge area. There are two outletts on the dash for defrost/defog of the windshield, and another near the deck under the steerring wheel.

            The Wallas furnaces do not come on and off like a house furnace. This is a problem because it creates a expansion and contracting of air making for cold spots. The Wallas units vary the heat output based on the thermostats call for heat. This creates a very even heat. As the boat warms the furnaces decrease their output. As the Boat cools they increase their output.

            I have found that at 32 degrees they are running on low to medium most of the time. At 10 degrees thay are running pretty much full blast to keep up. One time it was 7 degrees with a 40 knot wind and it was chilly. At that point I started the generator to keep the engine bay warm, and ran all four built in electric heaters to stay warm. That was frigging COLD. I ran the generator 24X7 for a whole week, very unheard of in Seward Alaska. The Liveaboard right next to me ran his main propulsion engines in gear for a week just to stay warm. (diffewrent boat brand,model)

            I can tell you that adding a full cockpit enclosure helped more than a person might think. That keeps the wind from all those windows in the aft section of the boat. I have also added weatherstripping to my lazarette hatches, and have heavy duty industrial throw rugs or runners over completely covering the deck in the cockpit.

            KEVIN SANDERS
            4788 LISAS WAY - SEWARD ALASKA
            where are we right now​​​​​​???​

            https://share.findmespot.com/shared/...j23OquWOj2N3Xe

            Comment


              #7
              That's great info. Thanks!

              I've been struggling to figure heat loss on the 4588 and was leaning towards one 40K hydronic unit with 7 fan modules.

              I can figure heat loss on a building - that's simple. Boat's not so much. I don't intend to spend winters in cold climates [got 9 inches of snow last night just north of Boston], but I can see myself transiting in cold weather in the 20's / 30's. I would not have thought 27K would be enough.

              Thanks again.
              1989 Bayliner 4588
              Portsmouth, NH

              Comment


                #8
                Most boats are poorly insulated. None, except fishing boats are insulated for Alaska or the northern US. Adding insulation helps to reduce your heating needs. Also window coverings. I have a private dock and 50 amp/240v service. While it's possible to heat my 83' boat with electricity, it's expensive and my power costs .0743/kwh. I have a wood stove, diesel stove and a pellet stove along with an oil fired boiler and hydronic system. The stoves all have a water coil that will heat the boiler. Wood pellets are, by far, the cheapest heat. Wood is only cheap if I cut, split and haul. While I have a place to store a winter's wood, traversing winter docks with arm loads of wood was a pia. I had some nice bruises to show for it. Now the wood stove is used to burn paper waste unless I run into some easy wood. The boiler isn't as efficient as a Webasco and others. It will burn 5+ gallons/day in 25° weather. The boiler and hydronic system was installed when diesel was about 35¢. When diesel hit $4 I added the pellet stove. In average winter temps in coastal Oregon, it costs about $7.50/day in pellets. That keeps about half the boat warm and the rest about 55-60°.

                Comment

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